Bug 1113425 part 1 - Fix some bad CSS comment syntax in animation tests; r=mattwoodrow

dom/animation/test/chrome/test_running_on_compositor.html

@@ -14,7 +14,7 @@
   to { transform: translate(100px) }
 }
 .target {
-  // Element needs geometry to be eligible for layerization
+  /* Element needs geometry to be eligible for layerization */
   width: 100px;
   height: 100px;
   background-color: white;

dom/animation/test/mozilla/test_deferred_start.html

@@ -11,7 +11,7 @@
   to { transform: translate(100px); }
 }
 .target {
-  // Element needs geometry to be eligible for layerization
+  /* Element needs geometry to be eligible for layerization */
   width: 100px;
   height: 100px;
   background-color: white;